Hydraulic torque converters, devices used to change the ratio of torque to speed between the input and output shafts of the converter, revolutionized the automotive and marine propulsion industries by providing hydraulic means to transfer energy from an engine to a drive mechanism, e.g., drive shaft or automatic transmission, while smoothing out engine power pulses. A torque converter includes three primary components: an impeller, sometimes referred to as a pump, directly connected to the engine's crankshaft; a turbine, similar in structure to the impeller, however the turbine is connected to the input shaft of the transmission; and, a stator, located between the impeller and turbine, which redirects the flow of hydraulic fluid exiting from the turbine prior to reentry into the pump, thereby providing additional rotational force to the pump. This additional rotational force results in torque multiplication. Thus, for example, when the impeller speed is high and the turbine speed is low, torque may be multiplied by a 2:1 or higher ratio, whereas when the impeller and turbine speeds are approximately the same, torque can be transferred at about a 1:1 ratio.
Conventional torque converters include two ports, or paths, available to input power to or extract power from the torque converters. Normally power is input from an engine's crankshaft, through a flexplate, and into the torque converter pump weldment. Power is extracted from the torque converter via the turbine, and is subsequently sent through the transmission input shaft, thereby driving the transmission.
A separate shaft emanating from the transmission, the stator shaft, enters the torque converter, however power is not transmitted through this path as the shaft is stationary. Often torque converters include a one-way clutch between the stator and the stationary shaft which permits the stator to rotate in response to changing fluid forces resulting from increased turbine speed, i.e., as the turbine speed increases in response to increased pump speed. Thus, when the pump rotates more quickly than the turbine, the stator remains stationary. While contrarily, as the turbine rotation speed approaches the speed of the pump, the stator begins to rotate due to increased fluid forces. When the turbine rotates at substantially the same speed as the pump, the stator freewheels, and as described supra, torque is transmitted at approximately a 1:1 ratio between the engine and the transmission. Accordingly, throughout the range where the rotation of the turbine is insufficient to drive the rotation of the stator, energy is lost which could be recovered provided the torque converter and transmission included means to transfer energy from the stator to the transmission.
FIG. 1 shows a lever diagram depicting the energy paths from an input shaft through a prior art transmission, while FIG. 2 depicts a cross sectional view of a torque converter and a prior art transmission arranged according to FIG. 1. One of ordinary skill in the art will recognize that lever diagrams are a common means of describing the interactions within planetary gear sets. Each lever includes one point where power is received, one point where power is transmitted, and a fulcrum point. In some embodiments, a fulcrum is disposed between the locations where power is received and transmitted, while in other embodiments, a fulcrum is located at an end of a lever and the locations of power receipt and transmission are along the length of the lever. The direction of lever movement, i.e., left to right and right to left when viewing FIG. 1, determines the direction of gear rotation. Each lever consists of two arms, i.e., the distance between the fulcrum point and location of power receipt and the distance between the fulcrum point and location of power transmission. The ratio between the two lever arms diagrammatically represents the gear ratio.
FIGS. 1 and 2 represent the teaching disclosed in U.S. Pat. No. 5,106,352, which teaching is incorporated herein by reference. It is well known in the art how to efficiently obtain six forward gears and one reverse gear from three epicyclic gear sets, three clutches and two braking devices. Transmission 10 broadly includes epicyclic gear sets 12, 14 and 16 and further includes clutches 18, 20 and 22, as well as braking clutches 24 and 26. Epicyclic gear set 12 comprises sun gear 28, planet gear carrier 30 and ring gear 32, epicyclic gear set 14 comprises sun gear 34, planet gear carrier 36 and ring gear 38, and epicyclic gear set 16 comprises sun gear 40, planet gear carrier 42 and ring gear 44. Transmission 10 receives power through input shaft 46 and transmits power through output shaft 48. In order to obtain six forward gears and one reverse gear, clutches 18, 20 and 22 and braking clutches 24 and 26 are configured in various combinations according to Table 1 below. An ‘X’ denotes an engaged clutch/braking clutch and a blank indicates a disengaged clutch/braking clutch.
TABLE 1BrakingBrakingGearClutch 18Clutch 20Clutch 22Clutch 24Clutch 26Forward 1XXForward 2XXForward 3XXForward 4XXForward 5XXForward 6XXReverseXX
FIG. 2 more fully describes the coupling of torque converter 50 to transmission 10. A rotary drive unit (not shown), e.g., a vehicle engine, is fixedly secured to drive plate 52 via studs 54. Drive plate 52 is secured to housing shell 56 of torque converter 50 via rivets 58, thereby enabling the transfer of power from the rotary drive unit to torque converter 50. Power is transferred within torque converter 50 by fluid. As torque converter 50 rotates, pump 60, fixedly connected to housing shell 56, transmits fluid to turbine 62. Upon exiting turbine 62, the fluid passes through stator 64 which redirects the flow of the fluid prior to reentry into pump 60. Turbine 62 is secured to hub 66, which in turn is rotationally engaged with input shaft 46. As described supra, input shaft 46 drives ring gear 32. Planet gear 68 is rotatably mounted to planet gear carrier 30 via shaft 70. Ring gear 32 is arranged to engage planet gear 68 and thus plant gear carrier 30. As shown in FIG. 1, power is introduced into transmission 10 through the previously described path, and subsequently, the desired gearing of transmission 10 is obtained by orienting the engagement/disengagement of clutches 18, 20 and 22 and braking clutches 24 and 26 according to Table 1.
One-way clutch 72 is operatively arranged between stator 64 and stator shaft 74. Stator shaft 74 is fixedly secured to casing segment 76, thereby precluding any movement and/or rotation of stator shaft 74. Similarly, movement of sun gear 28 is restricted by extension 78 which is integral to stator shaft 74. During periods of use when the rotational speed of turbine 62 is less than the rotational speed of pump 60, stator 64 is prevented from rotating via the interaction between one-way clutch 72 and stator shaft 74. As the ratio of rotational speeds between pump 60 and turbine 62 approaches unity, one-way clutch 72 permits stator 64 to freewheel, thus permitting it to rotate at a speed substantially similar to pump 60 and turbine 62. As described supra, energy imparted on stator 64 by the fluid is essentially lost due to the non-rotation of stator shaft 74.
As can be derived from the variety of devices and methods directed at providing means to couple a torque converter stator to a transmission, many means have been contemplated to accomplish the desired end, i.e., high efficiency coupling between an engine and a transmission, without sacrificing energy provided by the engine, and thus resulting in better fuel efficiency and performance. Heretofore, tradeoffs between efficiency of coupling and transmission design were required. Thus, there has been a longfelt need for a torque converter having a stator operatively arranged to transfer torque to the transmission, thereby recovering a larger portion of the energy produced by the engine.